Fuel cell-use carbon fiber woven fabric, electrode element, fuel cell mobile unit, and production method for fuel cell-use carbon fiber woven fabric

ABSTRACT

A fuel cell-use carbon fiber woven fabric, especially a carbon fiber woven fabric preferably used for the electrode diffusion layer of an electrode element in a fuel cell. The electrode diffusion layer of an electrode element in a fuel cell, requiring conductivity, gas diffusing/permeating features, and strength that withstands handling, is formed from carbon fiber woven fabrics as is widely known. The conventional carbon fiber woven fabric poses such problems that deformation by compression is large, the dimension of a fuel cell is significantly changed by pressurizing, irregularities by weave texture are large, and contact resistance is large. A carbon fiber woven fabric used for a fuel cell-use carbon fiber woven fabric has an average size of warps and wefts constituting the woven fabric of 0.005-0.028 g/m, and a woven density of the warps and/or wefts of 20 pieces/cm.

TECHNICAL FIELD

[0001] The present invention relates to a carbon fiber woven fabric tobe used in a fuel cell, an electrode element using the carbon fiberwoven fabric, a fuel cell using the electrode element, a mobile unitusing the fuel cell, and a method for producing a carbon fiber wovenfabric to be used in the fuel cell. The invention especially relates toa dense and thin carbon fiber woven fabric to be used in a fuel cell,which can be preferably used as the electrode diffusion layer of anelectrode element in a solid polymer electrolyte fuel cell.

BACKGROUND ART

[0002] An electrode diffusion layer of a fuel cell is required to allowdiffusion and permeation of substances participating in currentcollecting function and electrode reaction. Furthermore, a materialconstituting the electrode diffusion layer is required to have electricconductivity, gas diffusibility, gas permeability, strength to endurehandling, etc.

[0003] As the material used to form the electrode diffusion layer of afuel cell, a porous carbon plate comprising short carbon fibers boundwith carbon, described in JP-06-20710-A, JP-07-326362-A orJP-07-220735-A, is known. However, the porous carbon plate has suchproblems that it is difficult to produce the plate in a continuouslonger form and that the carbon used as a binder is likely to bedestroyed under the pressure acting when the electrode is produced orwhen the carbon plate is assembled into a cell.

[0004] As a material capable of being formed as a continuously longmaterial to be used for forming an electrode diffusion layer, a carbonfiber woven fabric is known. Examples of the carbon fiber woven fabricinclude “PANEX PWB-3” produced by Stackpole Fibers Company which isdescribed in U.S. Pat. No. 4,293,396 and “AVCARB” produced by TextronSpecialty Materials which is described in JP-10-261421-A.

[0005] The “PANEX PWB-3” can provide a continuously long material, butif the carbon fiber woven fabric is used as an electrode diffusionlayer, it has such problems that a dimension of fuel cell is greatlychanged under pressurization, and that separator grooves are filled withthe woven fabric, since the woven fabric is greatly deformed undercompression. Furthermore, it has a problem that since it is difficult toapply a catalyst layer because of the large undulation attributable toits weave texture, the contact resistance becomes large. Moreover, ithas a problem that a woven fabric formed of thick weaving yarns buthaving a low unit weight causes the catalyst layer to come off, sincethe gaps between fibers are large.

[0006] The invention has been completed in view of the above-mentionedproblems of the prior art. An object of the invention is to provide athin carbon fiber woven fabric slightly deformable under compression,small in electric resistance and suitable for use as an electrodediffusion layer in a fuel cell. Another object of the invention is toprovide an electrode element using a carbon fiber woven fabric to beused in a fuel cell of the invention, a fuel cell using the electrodeelement, and a mobile unit using the fuel cell. A further object of theinvention is to provide a method for producing a carbon fiber wovenfabric to be used in a fuel cell of the invention.

DISCLOSURE OF THE INVENTION

[0007] A carbon fiber woven fabric for a fuel cell of the invention ischaracterized in that the average fineness of the warp yarns and theweft yarns constituting the woven fabric is in the range of 0.005 to0.028 g/m, and that the weave density of the warp yarns and/or the weftyarns is not less than 20 yarns/cm.

[0008] It is preferred that the unit weight of the woven fabric is inthe range of 50 to 150 g/m².

[0009] It is preferred that the thickness of the woven fabric is in therange of 0.1 to 0.3 mm.

[0010] It is preferred that the value of N×W is not less than 0.6 whereN (yarns/cm) is the weave density of the warp yarns and/or weft yarnsand W (cm/yarn) is the yarn width.

[0011] It is preferred that the crush value the woven fabric undercompression is not more than 0.15 mm.

[0012] It is preferred that the warp yarns and/or the weft yarns arespun yarns.

[0013] It is preferred that the electric resistance of the woven fabricis not more than 30 mΩcm², and that the differential pressure causedwhen 14 cm³/cm²/sec of air is passed through the woven fabric in thethickness direction is not more than 5 mm Aq.

[0014] It is preferred that the ratio of the number of oxygen atoms tothe number of carbon atoms on the carbon fiber surfaces of the wovenfabric is not less than 0.06 and less than 0.17.

[0015] It is preferred that the woven fabric contains carbon black onits surfaces and/or inside.

[0016] It is preferred that the woven fabric contains a water-repellentsubstance.

[0017] An electrode element for a fuel cell of the invention is formedof the above-mentioned carbon fiber woven fabric for a fuel cell of theinvention.

[0018] It is preferred that the electrode element comprises an electrodediffusion layer formed of the above-mentioned carbon fiber woven fabricfor a fuel cell of the invention.

[0019] It is preferred that the electrode diffusion layer has a catalystlayer disposed thereon in layer.

[0020] It is preferred that the electrode diffusion layer has a catalystlayer and a polymer electrolyte film deposited thereon in layers.

[0021] A fuel cell of the invention comprises the above-mentionedelectrode element of the invention.

[0022] It is preferred that the fuel cell has a grooved separatorprovided on the electrode element.

[0023] A mobile unit of the invention is mounted with theabove-mentioned fuel cell.

[0024] A method for producing a carbon fiber woven fabric for a fuelcell of the invention comprises a pressurization step of pressurizing aprecursor fiber woven fabric composed of carbon precursor fibers in thethickness direction and a step of carbonizing the precursor fiber wovenfabric.

[0025] In the method for producing a carbon fiber woven fabric for afuel cell, it is preferred that the pressurization step is carried outat a heating temperature of not more than 300° C. at a pressure of 5 to500 kg/cm.

[0026] In the method for producing a carbon fiber woven fabric for afuel cell, it is preferred that the carbon precursor fibers are oxidizedacrylic fibers.

THE BEST MODES FOR CARRYING OUT THE INVENTION

[0027] In the carbon fiber woven fabric for a fuel cell of theinvention, it is necessary that the average fineness of the warp yarnsand the weft yarns constituting the woven fabric is in the range of0.005 to 0.028 g/m. It is preferable that the average fineness is in therange of 0.01 to 0.026 g/m, and more preferably in the range of 0.013 to0.022 g/m. An average fineness of more than 0.028 g/m is not preferred,since the woven fabric becomes thick or a space between weaving yarnsbecomes large.

[0028] If the unit weight of a woven fabric is A (g/m²), the density ofwarp yarns is Nw (yarns/cm), and the density of weft yarns is Nf(yarns/cm), then the average fineness can be obtained from the followingequation (I).

Average fineness (g/m)=A/(Nw+Nf)/100  (I)

[0029] In the carbon fiber woven fabric for a fuel cell of theinvention, it is necessary that the weave density of the warp yarnsand/or the weft yarns is not less than 20 yarns/cm.

[0030] It is preferable that the weave density is not less than 22yarns/cm. If the weave density is too low, the spaces between weavingyarns become large, and such problems are likely to occur that thecatalyst layer is likely to come off, and that since the electrolyticmembrane is likely to dry, high cell characteristics is cannot beobtained. It is especially preferable that both the warp yarns and theweft yarns have the weave density mentioned above. If the weave densityincreases, the weaving speed declines to raise the cost. It is,therefore, preferable that the weave density is not more than 35yarns/cm, and more preferably not more than 30 yarns/cm.

[0031] In the measurements of the average fineness and the weavedensity, in the case where the warp yarns and the weft yarns cannot beidentified which is which in the woven fabric, the yarns in a givendirection should be considered as warp yarns, and the yarns in the otherdirection, as weft yarns.

[0032] It is preferred that the unit weight of the carbon fiber wovenfabric for a fuel cell of the invention is in the range of 50 to 150g/m². A more preferred range is from 70 to 120 g/m², and a further morepreferred range is from 80 to 98 g/m².

[0033] In the case where the unit weight is too low, the spaces betweenthe weaving yarns constituting the woven fabric are so large that thereoccur such problems that the catalyst layer comes off and that since theelectrolytic membrane is likely to dry, high cell characteristics cannotbe obtained. In the case where the unit weight is too high, it isdifficult to produce the woven fabric, and the woven fabric tends to bethick. As a result, such problems are likely to occur that the fuel cellis dimensionally greatly changed under pressurization, and that theseparator grooves are likely to be filled with the woven fabric. In thecase where the woven fabric has carbon black, resin and the likedeposited, the weight excluding these deposits should be the weight ofthe carbon fiber woven fabric.

[0034] It is preferred that the thickness of the carbon fiber wovenfabric for a fuel cell of the invention is in the range of 0.1 to 0.3mm. A more preferred range is from 0.13 to 0.25 mm, and a further morepreferred range is from 0.15 to 0.20. The thickness refers to thethickness measured when a pressure of 0.15 MPa is applied to the carbonfiber woven fabric.

[0035] In the case where the thickness is too small, such a problemoccurs that since the electrolytic membrane is likely to dry, high cellcharacteristics cannot be obtained. Furthermore, in the case where thethickness is too large, such problems are likely to occur that the fuelcell is dimensionally greatly changed under pressurization, and that theseparator grooves are likely to be filled with the woven fabric.

[0036] If the weave density of the warp yarns and/or the weft yarns ofthe carbon fiber woven fabric for a fuel cell of the invention is N(yarns/cm) and the yarn width is W (cm/yarn), then it is preferred thatthe value of product N×W is not less than 0.6. More preferred is notless than 0.65, and further more preferred is not less than 0.7.

[0037] The yarn width W refers to the width viewed in the directionperpendicular to the face of the woven fabric. The yarn width W can alsobe measured with the woven fabric magnified as an SEM photograph, etc.It is preferred that the N×W values of both the warp yarns and the weftyarns are not less than 0.6 respectively.

[0038] In the case where the warp yarns cannot be distinguished from theweft yarns on the woven fabric as explained in the above, the yarns in agiven direction should be warp yarns, and the yarns in the otherdirection, weft yarns.

[0039] In the case where the value of N×W is too small, there occur suchproblems that since the spaces between weave yarns are large, thecatalyst layer comes off, that since the surface is rough, the contactbetween the catalyst layer and the separator is not sufficient, and thatsince the electrolytic membrane is likely to dry, high cellcharacteristics cannot be obtained. It is preferred that the value ofN×W is not more than 0.96. More preferred is not more than 0.90, andfurther more preferred is not more than 0.85. If the value of N×W is toohigh, weaving is so difficult as to lower the weaving speed, henceincreasing the cost.

[0040] It is preferred that the crush value of the carbon fiber wovenfabric for a fuel cell of the invention under compression is not morethan 0.15 mm. More preferred is not more than 0.12 mm, and further morepreferred is not more than 0.10 mm.

[0041] The crush value under compression refers to the differencebetween the thickness measured at a pressure of 0.15 MPa and thethickness measured at a pressure of 1.5 MPa. In the case where the crushvalue under compression is too large, there occur such problems thatstack clamping is difficult, that it is difficult to achieve a uniformheight, and that the woven fabric fills the separator grooves.

[0042] It is preferred that the warp yarns and/or the weft yarnsconstituting the carbon fiber woven fabric of the invention are spunyarns. Since spun yarns have many voids in them, higher air permeabilityand higher water permeability can be obtained.

[0043] It is preferred that the electric resistance of the carbon fiberwoven fabric for a fuel cell of the invention is not more than 30 mΩcm².More preferred is not more than 25 mΩcm², and further more preferred isnot more than 20 mΩcm². If the electric resistance is too high, thewoven fabric used in an electrode of a fuel cell increases the voltageloss.

[0044] The method for measuring electric resistance is as follows. Twoplates each of which is a vitreous carbon plate overlaid with a copperfoil, wherein the vitreous carbon plate has the width of 50 mm, lengthof 200 mm, thickness of 1.5 mm and a smooth surface, and the copper foilhas the width of 50 mm, length of 200 mm and thickness of 0.1 mm areprepared. The plates are called test electrodes. The two test electrodesare overlaid on each other with the vitreous carbon sheets facing eachother, to cross each other at their central portions. The carbon fiberwoven fabrics are cut to have area S (cm²), and the cut carbon fiberwoven fabrics are pressurized to apply a pressure of 0.98 MPa for thearea of the fabrics. At the ends on one side of the two test electrodes,current terminals are installed, and at the ends on the other side,voltage terminals are installed. Using the current terminals, a currentof 1 A is made to flow between the two test electrodes. The voltage V(V) across the voltage terminals is measured, to calculate resistance R(mΩcm²) from the following equation (II).

R=1,000V×S  (II)

[0045] It is preferred that the differential pressure is not more than 5mm Aq, when 14 cm³/cm²/sec of air is passed in the thickness directionof the carbon fiber woven fabric for a fuel cell of the invention. Amore preferred range is from 0.2 to 2 mm Aq, and a further morepreferred range is from 0.4 to 1.5 mm Aq. In the case where thedifferential pressure is too large, the air permeability, hydrogenpermeability and water permeability are low, and the cell voltage tendsto be low. In the case where the differential pressure is too small, thewater is likely to evaporate, and the resistance of the membrane tendsto be higher. In the case where carbon black, resin and the like aredeposited on the woven fabric, these deposits should be removed beforemeasuring the differential pressure.

[0046] It is preferred that the ratio of the number of oxygen atoms tothe number of carbon atoms on the surfaces of the carbon fibersconstituting the carbon fiber woven fabric for a fuel cell of theinvention is not less than 0.06 and less than 0.17. A more preferredrange is not less than 0.10 and not more than 0.16, and a further morepreferred range is not less than 0.11 and not more than 0.15.

[0047] The ratio (O/C) of the number of oxygen atoms to the number ofcarbon atoms on the surfaces of the carbon fibers constituting thecarbon fiber woven fabric is defined by the following equation.

O/C=(Rate of oxygen atoms on fiber surfaces)/(Rate of carbon fibers onfiber surfaces)

[0048] If the ratio O/C on the surfaces of carbon fibers is less than0.06, the fiber surfaces are low in hydrophilicity, and the migration ofwater in the yarns owing to the capillary tubes formed by plural carbonfibers tends to decrease. As a result, the extra water in the systemcannot be efficiently discharged, and the water produced due to thepower generation reaction is accumulated to clog the cathode electrodewith water with a tendency of lowering the gas diffusibility.

[0049] If the ratio O/C on the surfaces of carbon fibers is not lessthan 0.17, the fiber surfaces become too high in hydrophilicity.Therefore, even in the case where the quantity of produced water issmall, the cathode electrode can be clogged with water with a tendencyof lowering the gas diffusibility. If the ratio O/C is in the rangementioned above, the surfaces of the fibers constituting the carbonfiber woven fabric for a fuel cell of the invention are moderatelyhydrophilic. Therefore, the water can highly migrate in the woven fabricowing to the capillary tubes formed by plural carbon fibers, to give afeature that the cathode electrode is unlikely to be clogged with water.For this reason, the extra water in the system can be efficientlydischarged, to allow excellent water control.

[0050] The ratio of the number of oxygen atoms to the number of carbonatoms on the surfaces of carbon fibers can be measured by X-rayphotoelectron spectroscopy.

[0051] It is preferred that the carbon fiber woven fabric for a fuelcell of the invention contains carbon black on its surfaces and/orinside for the purposes of increasing electric conductivity, smootheningthe surfaces and controlling the water permeability. The method foradding carbon black is not especially limited, but it is preferred thatcarbon black is bound to the woven fabric using a resin or the like asan adhesive.

[0052] It is preferred that the carbon fiber woven fabric for a fuelcell of the invention contains a water-repellent substance for thepurpose of preventing clogging with water when it is used in a fuelcell. Furthermore, a water-repellent substance can also be used as anadhesive for the carbon black. The water-repellent substance is notespecially limited, and for example, a fluorine-containing compound,silicon-containing compound or the like can be preferably used.

[0053] The method for producing the carbon fiber woven fabric for a fuelcell of the invention is not especially limited. For example, yarnsconsisting of carbon fibers can be woven to produce a carbon fiber wovenfabric, or carbon precursor fibers can also be woven to produce aprecursor fiber woven fabric that is then carbonized into a carbon fiberwoven fabric. As another method, a commercially available precursorfiber woven fabric can also be carbonized to produce a carbon fiberwoven fabric. In the case where yarns consisting of carbon fibers arewoven, it is likely to occur that the carbon fibers are broken orfolded. Furthermore, the warp yarns and the weft yarns are likely to beshifted to deform the meshes of the produced carbon fiber woven fabric,and the warp yarns and the weft yarns at the edges of the woven fabricare likely to come off. Therefore, the latter method of carbonizing acarbon precursor fiber woven fabric is preferred.

[0054] The carbon fibers or precursor fibers of carbon fibers used forproducing the carbon fiber woven fabric for a fuel cell of the inventionare not especially limited. Examples of them includepolyacrylonitrile-based carbon fibers, rayon-based carbon fibers,phenol-based carbon fibers, pitch-based carbon fibers, oxidized acrylicfibers, rayon fibers, phenol fibers, infusible pitch fibers, etc. Anespecially preferred method is to carbonize the woven fabric produced byweaving oxidized acrylic fibers.

[0055] In the process for producing the carbon fiber woven fabric for afuel cell of the invention, it is preferred to include a step ofpressurizing in the thickness direction, the woven fabric produced byweaving carbon precursor fibers, since the crush value under compressioncan be kept small, for example, when plural electrode diffusion layersformed of carbon fiber woven fabrics are laminated for producing a fuelcell.

[0056] It is preferred that the pressurization in the thicknessdirection is carried out before or during carbonization. Thepressurization before or during carbonization is more effective inlessening the crush value under compression than the pressurizationafter carbonization.

[0057] The method of pressurizing before carbonization can be acontinuous pressurization method using a roll press or belt press or asurface load pressurization method using a batch press or load. In viewof the efficiency of the pressurization step, it is preferred to use aroll press or belt press that allows continuous pressurization.

[0058] It is preferred that the temperature during pressurization is notmore than 300° C. A more preferred range is from 150 to 250° C., and afurther more preferred range is from 170 to 230° C. In the case wherethe temperature is too low, the deformation under compression is toosmall, and the effect of reducing the thickness cannot be sufficientlyobtained. In the case where oxidized acrylic fibers are used, aremarkable pressurization effect can be observed at 150° C. or higher.In the case where the temperature is too high, since the oxidation ofcarbon precursor fibers in air takes place, the pressurization must becarried out in an inactive atmosphere. Furthermore, because of hightemperature, equipment maintenance and process control become difficult.In the case of oxidized acrylic fibers, the problems of oxidation anddeterioration do not occur at 250° C. or lower, since the fibersunderwent flame-retarding treatment.

[0059] In the case where the pressurization is carried out using rolls,it is preferred that the surface of at least one of the two rolls usedfor pressurization is made of a soft material such as rubber, resin,paper or nonwoven fabric for preventing the breaking of carbon precursorfibers and the decline of tensile strength. It is preferred that theline load of pressurization is in the range of 10 to 500 kg/cm. A morepreferred range is from 50 to 300 kg/cm, and a further more preferredrange is from 150 to 200 kg/cm.

[0060] In the case where hard rolls made of a metal or the like are usedfor pressurization, it is preferred that a clearance of 50 μm or more isestablished or that the line load is kept in the range of 5 to 200kg/cm, for preventing the destruction of the woven fabric, the breakingof the fibers of the woven fabric, and the decline of tensile strength.A more preferred range of line load is from 10 to 100 kg/cm, and afurther more preferred range is from 20 to 70 kg/cm.

[0061] In the case where a surface load is used for pressurization, itis preferred that the pressure is 5 MPa or more.

[0062] In the case where a woven fabric of carbon precursor fibers ispressurized while being carbonized, it is only required that thepressurization is carried out at least at any moment in thecarbonization step. In the case where preliminary carbonization at thehighest temperature of about 500 to 1,000° C. is followed by regularcarbonization at the highest temperature of higher than 1,000° C. forcarrying out carbonization twice, it is preferred that the woven fabricis pressurized during at least either preliminary carbonization orregular carbonization. The method of pressurization can be a continuouspressurization using rolls or belt, or a surface load pressurization, ora method of carbonizing a rolled woven fabric for pressurization usingthe tension of rolling and the tension caused by the shrinkage duringcarbonization, though the method is not limited to these methods.

[0063] In the case where a rolled woven fabric of carbon precursorfibers is carbonized, it is preferred that the outermost layer of theroll is covered with paper, film or woven fabric with a surface smootherthan the woven fabric, since the woven fabric can be carbonized withoutwrinkling even at the outermost layer. More particularly it is preferredto cover the woven fabric of carbon precursor fibers with paper, film orwoven fabric made of carbon or any other material capable of beingcarbonized and incapable of molten when carbonized, such as a polyimide,cellophane or cellulose.

[0064] In the case where a woven fabric of carbon precursor fibers iscarbonized and subsequently pressurized, it is preferred to pressurizewith the woven fabric wetted with a liquid substance such as water ororganic solvent, or to pressurize the woven fabric having a resin suchas a fluorine resin deposited. It is more preferred that a carbonizedwoven fabric having a resin deposited is pressurized at higher than itsmelting point or thermal deformation temperature.

[0065] In the carbon fiber woven fabric for a fuel cell of theinvention, the carbon produced when an organic material deposited on thecarbon fibers or carbon precursor fibers is carbonized, can also remaindeposited. The deposited carbon has an effect of inhibiting thedeformation under the pressurization of the carbon fiber woven fabric,but on the other hand, has a problem of lowering the gas permeabilityand the flexibility of the woven fabric. Therefore, it is preferred thatthe amount of the carbon is 20 wt % or less. More preferred is 5 wt % orless, and further more preferred is 2 wt % or less.

[0066] The carbon fiber woven fabric for a fuel cell of the inventioncan be preferably used as an electrode component such as a gas diffusionelectrode for a fuel cell, since it has electric conductivity and fluidpermeability.

[0067] Furthermore, the carbon fiber woven fabric for a fuel cell of theinvention can be preferably used as a conductive sheet to be used in afuel cell, especially as an electrode diffusion layer of a fuel cell. Itcan be especially suitably used as an electrode diffusion layer of afuel cell having a grooved separator. In the case where a groovedseparator is used as passages for feeding oxygen and a fuel to a fuelcell electrode, if the crush value of the carbon fiber woven fabricunder compression is large, the portions of the woven fabric facing thegrooves and hence not subjected to compression go into the grooves, toinhibit the function as the passages of oxygen and fuel. The carbonfiber woven fabric for a fuel cell of the invention, that is thin inthickness and small in the crush value under compression, caneffectively avoid inhibiting the passage function. As a result, thegrooves can have a smaller depth and the device can be made morecompact.

[0068] Moreover, the carbon fiber woven fabric for a fuel cell of theinvention can be preferably used as an electrode diffusion layer havinga catalyst layer disposed thereon as a layer or having a catalyst layerand a polymer electrolyte membrane disposed thereon as layers to form aunit. Still furthermore, the electrode diffusion layer or the unit canbe preferably used as a component of a fuel cell. The fuel cellcontaining the carbon fiber woven fabric for a fuel cell of theinvention, which is flexible and small in the crush value undercompression, is strong against vibration and impact, is compact, and issuitable as a fuel cell for a mobile unit. It is especially suitable asa fuel cell for a mobile unit requiring a compact fuel cell, above all,for a motor vehicle or two-wheeled car.

[0069] Examples are described below. The properties described in theexamples were measured according to the following methods.

[0070] Crush Value Under Compression:

[0071] A carbon fiber woven fabric was placed on a smooth table, and amicrometer indenter having a diameter of 5 mm was allowed to descendfrom above. With a load applied to the indenter, the thickness wasmeasured at a pressure of 0.15 MPa, and with the load further increased,the thickness was measured at a pressure of 1.5 MPa. The differencebetween the thickness measured at a pressure of 0.15 MP and thethickness measured at a pressure of 1.5 MPa was identified as the crushvalue. A smaller crush value is more desirable.

[0072] Electric Resistance:

[0073] The method described before was used to obtain the electricresistance from the following equation. A lower electric resistance ismore desirable.

R=1,000V×S

[0074] where R: Resistance (mΩcm²)

[0075] V: Voltage across voltage terminals (V)

[0076] S: Area of carbon fiber woven fabric (cm²)

[0077] Voltage at 0.7 A/cm²:

[0078] A carbon fiber woven fabric was coated with a mixture consistingof carbon black and polytetrafluoroethylene, and the coated fabric washeat-treated at 380° C., to produce a woven fabric having a carbonlayer. The deposited amount of the mixture consisting of carbon blackand polytetrafluoroethylene was about 2 mg/cm².

[0079] On the other hand, a mixture consisting of platinum-loaded carbonas a catalyst and Nafion was deposited on both sides of Nafion 112(produced by E. I. du Pont de Nemours and Company), to prepare amembrane-catalyst sheet. The amount of platinum as a catalyst was about0.5 mg/cm².

[0080] The membrane-catalyst sheet was held between two carbon-layeredwoven fabrics having the carbon layers turned inside, and the laminatewas heated at 130° C. and pressurized at 3 MPa for integration, toobtain a membrane-electrode assembly (MEA).

[0081] The MEA was held between grooved separators, and the cellcharacteristics were measured according to a conventional method. Thecell temperature was 70° C., and the temperature at which hydrogen gaswas applied was 80° C., while the temperature at which air was appliedwas 60° C. The gas pressure was atmospheric pressure. At 0.7 A/cm², thehydrogen availability was 70% and the air availability was 40%. A highervoltage is more desirable. At 0.7 A/cm², 0.5 V or higher is acceptable.

[0082] Tensile Strength:

[0083] A woven fabric was cut to have a dimension of 5 to 7 cm in thewarp direction and a dimension of 1.5 to 1.7 cm in the weft direction.Several warp yarns at both the edges in the weft direction were removed,to ensure that there were no broken warp yarns in the sample having alength of 5 to 7 cm. The width across the remaining warp yarns of thesample was measured as a sample width, and a tensile test was carriedout at a span of 3 cm and tensile speed of 1 mm/min. The value obtainedby dividing the maximum load (kg) by the sample width (cm) wasidentified as the tensile strength.

EXAMPLES 1, 2, 3, 4 and 5

[0084] Spun yarns of oxidized acrylic fibers (“Lastan” produced by AsahiKasei Corp., 1/34 Nm=0.029 g/m) were woven into a plain weave. The wovenfabric was carbonized in two steps at the highest temperatures of 650°C. and 1,950° C. in an inactive atmosphere, to obtain a carbon fiberwoven fabric. The unit weight and weave densities of each oxidizedacrylic fiber woven fabric, and the unit weight, weave densities,average weave density N, fineness, thickness, weaving yarn width W andthe value of N×W of each carbon fiber woven fabric are shown in Table 1.

EXAMPLE 6

[0085] Spun yarns of oxidized acrylic fibers (produced by Asahi KaseiCorp., 1/34 Nm=0.029 g/m) were used as warp yarns and spun yarns ofoxidized acrylic fibers (produced by Asahi Kasei Corp., 2/34 Nm=0.059Nm) were used as weft yarns to produce a plain weave. The woven fabricwas carbonized in two steps at the highest temperatures of 650° C. and1,950° C. in an inactive atmosphere, to obtain a carbon fiber wovenfabric. The unit weight and weave densities of the oxidized acrylicfiber woven fabric, and the unit weight, weave densities, average weavedensity N, fineness, thickness, weaving yarn width W and the value ofN×W of the carbon fiber woven fabric are shown in Table 1.

EXAMPLE 7

[0086] Oxidized acrylic fibers (produced by Toray Industries, Inc.) werespun into yarns by a draft zone system spinning. The fineness of thespun yarns was 1/40 Nm=0.025 g/m. The spun yarns were woven into a plainweave. The woven fabric was carbonized in two steps at the highesttemperatures of 650° C. and 1,950° C. in an inactive atmosphere, toobtain a carbon fiber woven fabric. The unit weight and weave densitiesof the oxidized acrylic fiber woven fabric, and the unit weight, weavedensities, average weave density N, fineness, thickness, weaving yarnwidth W and the value of N×W of the carbon fiber woven fabric are shownin Table 1.

EXAMPLE 8

[0087] The oxidized acrylic fiber woven fabric of Example 1 was heldbetween carbon sheets, carbonized at the highest temperature of 800° C.in an inactive atmosphere with a pressure of 2.8 g/cm² applied to thewoven fabric, depressurized and carbonized at 1,950° C., to obtain acarbon fiber woven fabric. The unit weight and weave densities of theoxidized acrylic fiber woven fabric, and the unit weight, weavedensities, average weave density N, fineness, thickness, weaving yarnwidth W and the value of N×W of the carbon fiber woven fabric are shownin Table 1.

EXAMPLE 9

[0088] The oxidized acrylic fiber woven fabric of Example 1 was fedthrough a roll press consisting of one iron roll and one rubber roll(iron roll 200° C., rubber roll 120° C.), to be pressurized at 200kg/cm. The woven fabric was carbonized in two steps at the highesttemperatures of 650° C. and 1,950° C. in an inactive atmosphere, toobtain a carbon fiber woven fabric. The unit weight and weave densitiesof the oxidized acrylic fiber woven fabric, and the unit weight, weavedensities, average weave density N, fineness, thickness, weaving yarnwidth W and the value of N×W of the carbon fiber woven fabric are shownin Table 1.

EXAMPLES 10, 11, 12, 13 and 14

[0089] The oxidized acrylic fiber woven fabric of Example 5 was fedthrough a roll press consisting of two iron rolls (roll temperature 60,100, 125, 150 or 200° C.), to be pressurized at 50 kg/cm. The wovenfabric was carbonized at the highest temperature of 1,950° C. in vacuum,to obtain a carbon fiber woven fabric. The unit weight and weavedensities of the oxidized acrylic fiber woven fabric, and the unitweight, weave densities, average weave density N, fineness and thicknessof each carbon fiber woven fabric are shown in Table 1.

EXAMPLES 15, 16, 17 and 18

[0090] The oxidized acrylic fiber woven fabric of Example 5 was fedthrough a roll press consisting of two iron rolls (roll temperature 200°C.), to be pressurized at 11, 100, 150 or 250 kg/cm. The woven fabricwas carbonized at the highest temperature of 1,950° C. in vacuum, toobtain a carbon fiber woven fabric. The unit weight and weave densitiesof the oxidized acrylic fiber woven fabric, and the unit weight, weavedensities, average weave density N, fineness and thickness of eachcarbon fiber woven fabric are shown in Table 1.

EXAMPLE 19

[0091] The oxidized acrylic fiber woven fabric of Example 5 was fedthrough a roll press consisting of two iron rolls (roll temperature 200°C.) having a clearance of 150 μm, to be pressurized at 250 kg/cm. Thewoven fabric was carbonized at the highest temperature of 1,950° C. invacuum, to obtain a carbon fiber woven fabric. The unit weight and weavedensities of the oxidized acrylic fiber woven fabric, and the unitweight, weave densities, average weave density N, fineness and thicknessof the carbon fiber woven fabric are shown in Table 1.

EXAMPLE 20

[0092] In a beaker containing 500 ml of 0.1 N sulfuric acid, a carbonsheet was used as the cathode, and the carbon fiber woven fabric ofExample 4 cut into a size of 8 cm×8 cm was used as the anode, forcarrying out electrolytic treatment with a current of 48 mA kept flowingfor 125 seconds. After completion of electrolytic treatment, the carbonfiber woven fabric was washed with purified water, and dried in a 100°C. oven for 10 minutes, to obtain a carbon fiber woven fabric treated tobe hydrophilic.

EXAMPLE 21

[0093] In a beaker containing 500 ml of 0.1 N sulfuric acid, a carbonsheet was used as the cathode, and the carbon fiber woven fabric ofExample 4 cut into a size of 8 cm×8 cm was used as the anode, forcarrying out electrolytic treatment with a current of 48 mA kept flowingfor 250 seconds. After completion of electrolytic treatment, the carbonfiber woven fabric was washed with purified water, and dried in a 100°C. oven for 10 minutes, to obtain a carbon fiber woven fabric treated tobe hydrophilic.

COMPARATIVE EXAMPLE 1

[0094] Spun yarns of oxidized acrylic fibers (produced by Asahi KaseiCorp., 2/34 Nm=0.059 g/m) were woven into a plain weave. The wovenfabric was carbonized in two steps at the highest temperatures of 650°C. and 1,950° C. in an inactive atmosphere, to obtain a carbon fiberwoven fabric. The unit weight and weave densities of the oxidizedacrylic fiber woven fabric, and the unit weight, weave densities,average weave density N, fineness, thickness, weaving yarn width W andthe value of N×W of the carbon fiber woven fabric are shown in Table 1.

COMPARATIVE EXAMPLE 2

[0095] Torayca Cloth (produced by Toray Industries, Inc.) “CO6349B” washeated at 1,400° C. in an inactive atmosphere, to is remove the sizingagent. The unit weight, weave densities, average weave density N,fineness, thickness, weaving yarn width W and the value of N×W of thecarbon fiber woven fabric are shown in Table 1.

COMPARATIVE EXAMPLE 3

[0096] In a beaker containing 500 ml of 0.1 N sulfuric acid, a carbonsheet was used as the cathode, and the carbon fiber woven fabric ofExample 4 cut into a size of 8 cm×8 cm was used as the anode, forcarrying out electrolytic treatment with a current of 48 mA kept flowingfor 500 seconds. After completion of electrolytic treatment, the carbonfiber woven fabric was washed with purified water, and dried in a 100°C. oven for 10 minutes, to obtain a carbon fiber woven fabric treated tobe hydrophilic.

[0097] For the carbon fiber woven fabrics obtained in Examples 1 to 21and Comparative Examples 1 to 3, the respective values of the crushvalue under compression, electric resistance, and differential pressurein air permeation are shown in Table 2, together with the values of thevoltage measured with a current of 0.7 A/cm² in the solid polymerelectrolyte fuel cells produced using the respective woven fabrics. Inthe woven fabric of Comparative Example 1, the applied carbon black andpolytetrafluoroethylene were separated from the woven fabric, not allowthe cell characteristics to be measured.

[0098] As can be seen from Tables 1 and 2, the carbon fiber wovenfabrics for a fuel cell of the invention were thin and small in thecrush value under compression, showing good cell characteristics. On theother hand, the woven fabrics of Comparative Examples 1 and 2 having anaverage fineness of more than 0.03 g/m were inferior in cellcharacteristics. That is, the woven fabric of Comparative Example 1 wasrelatively thick and large in the crush value under compression. Thewoven fabric of Comparative Example 2 was as low as 0.44 V in voltage.

[0099] From the comparison of Examples 5 and 10 to 14, it can be seenthat pressing can reduce the thickness, to make the crush value undercompression small, and that the effect of thinning at 150° C. or higheris remarkable.

[0100] From the comparison of Examples 5 and 14 through 19, it can beseen that if the pressure of a roll press consisting of two metallicrolls is raised, the thickness is reduced to make the crush value undercompression small. On the other hand, as shown in Table 3, if thepressure is raised especially to 100 kg/cm or higher, it is necessary toestablish a clearance between the rolls and to select an adequatepressure, since otherwise the tensile strength of the woven fabricdeclines.

[0101] As shown in Table 4, since the woven fabrics of Examples 15 and16 are adequately hydrophilic on the fiber surfaces, their voltages were0.61 V and 0.62 V respectively, being higher than 0.60 V of Example 4.On the other hand, in Comparative Example 3, since the ratio O/C was0.17, the hydrophilicity on the fiber surfaces was so high that thevoltage was as low as 0.41 V. TABLE 1 Oxidized fiber woven fabric Carbonfiber woven fabric Weave density Weave density Warp Weft Unit Unit WarpWeft Average yarns yarns weight weight yarns yarns Average weavefineness Thickness Width W (yarns/cm) (yarns/cm) (g/m²) (g/m²)(yarns/cm) (yarns/cm) density (yarns/cm) (g/m) (mm) (cm) N × W Example 117.0 17.5 104 72 20.0 20.0 20.0 0.018 0.19 0.028 0.56 Example 2 24.023.0 157 99 28.0 26.0 27.0 0.018 0.22 0.028 0.76 Example 3 24.0 17.5 14088 27.0 20.5 24.0 0.019 0.22 0.028 0.67 Example 4 22.0 22.0 150 93 25.525.5 25.5 0.018 0.24 0.030 0.77 Example 5 22.5 20.0 146 91 25.0 22.524.0 0.019 0.22 0.028 0.67 Example 6 14.0 18.0 164 102 16.5 20.0 18.00.028 0.25 0.040 0.72 Example 7 23.0 20.0 126 86 27.0 25.0 26.0 0.0170.23 0.026 0.68 Example 8 17.0 17.5 104 66 20.0 19.0 19.5 0.017 0.180.025 0.49 Example 9 22.0 22.0 150 92 25.0 25.5 25.5 0.018 0.20 0.0370.94 Example 10 22.5 20.0 146 91 25.0 22.5 24.0 0.019 0.21 — — Example11 22.5 20.0 146 91 25.0 22.5 24.0 0.019 0.20 — — Example 12 22.5 20.0146 91 25.0 22.5 24.0 0.019 0.20 — — Example 13 22.5 20.0 146 89 25.022.5 24.0 0.019 0.18 — — Example 14 22.5 20.0 146 89 25.0 22.5 24.00.019 0.17 — — Example 15 22.5 20.0 146 90 25.0 22.5 24.0 0.019 0.18 — —Example 16 22.5 20.0 146 88 25.0 22.5 24.0 0.019 0.16 — — Example 1722.5 20.0 146 88 25.0 22.5 24.0 0.019 0.15 — — Example 18 22.5 20.0 14687 25.0 22.5 24.0 0.018 0.14 — — Example 19 22.5 20.0 146 89 24.5 22.524.0 0.019 0.19 — — Example 20 22.0 22.0 150 93 25.5 25.5 25.5 0.0180.24 0.030 0.77 Example 21 22.0 22.0 150 93 25.5 25.5 25.5 0.018 0.240.030 0.77 Oxidized fiber woven fabric Carbon fiber woven fabric Weavedensity Unit weight Warp Weft Unit Weave Warp Weft Average yarns yarnsweight density yarns yarns Average weave fineness Thickness Width W(yarns/cm) (yarns/cm) (g/m²) (g/m²) (yarns/cm) (yarns/cm) density(yarns/cm) (g/m) (mm) (cm) N × W Comparative 17.0 15.5 213 133 19.0 17.018.0 0.037 0.31 0.050 0.90 Example 1 Comparative — — — 120 9.0 9.0 9.00.066 0.14 0.104 0.94 Example 2 Comparative 22.0 22.0 150 93 25.5 25.525.5 0.018 0.24 0.030 0.77 Example 3

[0102] (Note: In the carbon fiber woven fabrics of Examples 9 and 10 ofTable 1, the warp yarns could not be distinguished from weft yarns.)TABLE 2 Carbon fiber woven fabric Crush value Differential underElectric pressure in air compression resistance permeation Voltage at(mm) (mΩcm) (mmAq) 0.7 A/cm² (V) Example 1 0.09  9 0.2 0.51 Example 20.10 11 1.8 0.57 Example 3 0.10 11 0.6 0.60 Example 4 0.11 10 1.1 0.60Example 5 0.11 10 1.1 0.60 Example 6 0.11 11 1.0 0.55 Example 7 0.12 110.7 0.58 Example 8 0.07 12 0.2 0.52 Example 9 0.09 10 1.4 0.58 Example10 0.08 10 1.3 — Example 11 0.07 10 1.4 — Example 12 0.07 10 1.5 —Example 13 0.06 10 1.7 — Example 14 0.05 10 1.9 — Example 15 0.07 10 — —Example 16 0.05 10 — — Example 17 0.05 10 — — Example 18 0.05 10 — —Example 19 0.07 10 — — Example 20 0.11 10 1.1 0.61 Example 21 0.11 101.1 0.62 Comparative 0.16 10 2.4 — Example 1 Comparative 0.03  8 1.60.44 Example 2 Comparative 0.11 10 1.1 0.41 Example 3

[0103] TABLE 3 Press pressure Clearance Tensile strength (kg/cm) (μm)(kg/cm) Example 5 — — 2.5 Example 14  50 0 2.6 Example 15  11 0 2.7Example 16 100 0 2.1 Example 17 150 0 1.7 Example 18 250 0 1.1 Example19 250 150  2.7

[0104] TABLE 4 Number of oxygen atoms/ Number of carbon atoms (O/C)Example 4 0.01 Example 20 0.11 Example 21 0.15 Comparative 0.17 Example3

Industrial Applicability

[0105] Since the carbon fiber woven fabric for a fuel cell of theinvention is a thin and dense woven fabric having a small fineness, itcan be slightly deformed under compression and is small in the spacesbetween the fibers and in undulation. Therefore, it can be suitably usedas an electrode diffusion layer to be used in a fuel cell.

1. A carbon fiber woven fabric for a fuel cell, characterized in thatthe average fineness of the warp yarns and the weft yarns constitutingthe woven fabric is in the range of 0.005 to 0.028 g/m, and that theweave density of the warp yarns and/or the weft yarns is not less than20 yarns/cm.
 2. A carbon fiber woven fabric for a fuel cell, accordingto claim 1, wherein the unit weight of the woven fabric is in the rangeof 50 to 150 g/m².
 3. A carbon fiber woven fabric for a fuel cell,according to claim 1 wherein the thickness of the woven fabric is in therange of 0.1 to 0.3 mm.
 4. A carbon fiber woven fabric for a fuel cell,according to claim 1, wherein the value of N×W is not less than 0.6where N (yarns/cm) is the weave density of the warp yarns and/or theweft yarns and W (cm/yarn) is the yarn width.
 5. A carbon fiber wovenfabric for a fuel cell, according to claim 1, wherein the crush value ofthe woven fabric under compression is not more than 0.15 mm. 6 A carbonfiber woven fabric for a fuel cell, according to claim 1, wherein thewarp yarns and/or the weft yarns are spun yarns. 7 A carbon fiber wovenfabric for a fuel cell, according to claim 1, wherein the electricresistance of the woven fabric is not more than 30 mΩcm², and thedifferential pressure caused when 14 cm³/cm²/sec of air is passedthrough the woven fabric in the thickness direction is not more than 5mm Aq.
 8. A carbon fiber woven fabric for a fuel cell, according toclaim 1, wherein the ratio of the number of oxygen atoms to the numberof carbon atoms on the carbon fiber surfaces of the woven fabric is notless than 0.06 and less than 0.17.
 9. A carbon fiber woven fabric for afuel cell, according to claim 1, wherein the woven fabric containscarbon black on its surfaces and/or inside.
 10. A carbon fiber wovenfabric for a fuel cell, according to claim 1, wherein the woven fabriccontains a water-repellent substance.
 11. An electrode element for afuel cell, formed of the carbon fiber woven fabric as set forth in anyone of claims 1 through
 10. 12. An electrode element for a fuel cell,comprising an electrode diffusion layer formed of the carbon fiber wovenfabric as set forth in any one of claims 1 through
 10. 13. An electrodeelement for a fuel cell, according to claim 12, wherein the electrodediffusion layer has a catalyst layer disposed thereon in layer.
 14. Anelectrode element for a fuel cell, according to claim 12, wherein theelectrode diffusion layer has a catalyst layer and a polymer electrolytemembrane disposed thereon in layers.
 15. A fuel cell comprising theelectrode element as set forth in claim
 11. 16. A fuel cell, accordingto claim 15, wherein a grooved separator is provided on the electrodeelement.
 17. A mobile unit mounted with the fuel cell as set forth inclaim
 15. 18. A method for producing a carbon fiber woven fabric for afuel cell, comprising a pressurization step of pressurizing a precursorfiber woven fabric composed of carbon precursor fibers in the thicknessdirection, and a step of carbonizing the precursor fiber woven fabric.19. A method for producing a carbon fiber woven fabric for a fuel cell,according to claim 18, wherein the pressurization step is carried out ata heating temperature of not more than 300° C. at a pressure of 5 to 500kg/cm.
 20. A method for producing a carbon fiber woven fabric for a fuelcell, according to claim 18 or 19, wherein the carbon precursor fibersare oxidized acrylic fibers.